A tripod type constant-velocity universal joint is heretofore known in which three axially extending track grooves are formed in the inner periphery of an outer ring, a pair of circumferentially opposed roller guide surfaces are formed for each track groove, three trunnions are provided on a tripod member mounted in the outer ring at positions corresponding to the track grooves, and spherical rollers rotatably supported by the respective trunnions are arranged in the track grooves to transmit torque between the outer ring and the tripod member at the engaging portions between the spherical rollers and the roller guide surfaces of the track grooves.
In this tripod type constant-velocity universal joint, when torque is transmitted with the outer ring and tripod member forming a working angle, the center of rotation of each spherical roller is inclined relative to the longitudinal direction of the corresponding track groove, so that due to the inclination, the spherical rollers do not make a pure rolling motion but relative slip occurs between the spherical rollers and the roller guide surfaces of the track grooves.
Thus, the frictional resistance at the contact portions between the spherical rollers and the roller guide surfaces increases, so that the sliding resistance is large while the outer ring and the tripod member are moving axially relative to each other. Vibration and noise thus develop, thus lowering the NVH (noise, vibration and harshness) characteristics.
In order to improve the NVH characteristics, in the tripod type constant-velocity universal joint described in JP patent publication 64-5164, axially extending raceway grooves are formed in circumferentially opposed sides of the track grooves formed in the outer ring, raceway grooves are formed in both sides of guide blocks relatively pivotally supported in the moving direction of the tripod member by the trunnions of the tripod member, and a plurality of balls are mounted between the former grooves and the latter grooves to transmit torque between the outer ring and the tripod member through the balls.
In this tripod type constant-velocity universal joint, even when the outer ring and the tripod member form a working angle, the guide blocks are held in a constant position by the balls disposed between the raceway grooves of the guide blocks and the raceway grooves of the outer ring. Thus, during relative axial movement between the outer ring and the tripod member, the balls roll with no vibration or noise produced. Thus, it has good NVH characteristics.
In the tripod type constant-velocity universal joint described in the above publication, it is necessary to provide portions for preventing the balls from coming out at both ends of the raceway grooves of the guide blocks. Thus, if the working angle between the outer ring and the tripod member increases, the balls may touch these portions, and cannot smoothly roll. The balls thus slip, so that in such a slip area, the NVH characteristics tend to worsen.
In order to solve this problem, in the constant-velocity universal joint described in JP patent publication 4-74565, a plurality of balls mounted between the raceway grooves of the guide blocks and the raceway grooves on both sides of the outer ring track grooves are retained by retainers, and the moving amount of each retainer is restricted to half the moving amount of the guide block by a moving amount restricting means so that the balls always roll.
In the tripod type constant-velocity universal joint described in JP patent publication 4-74565, since the moving amount restricting means for restricting the moving amount of the retainers have such a structure that a pinion is mounted to each retainer, and racks that mesh with the pinion are mounted to the outer ring and each guide block, the mechanism is complicated. Also, since a space for mounting the pinion and the pair of racks is needed between both sides of each guide block and the sides of the corresponding track groove, the constant-velocity universal joint becomes large.
An object of this invention is to simplify the structure and reduce the size of a tripod type constant-velocity universal joint in which the rolling elements for transmitting torque such as balls are retained by retainers, and the moving amount of the retainers are restricted to half the moving amount of the guide blocks.